This invention relates to an X-ray image intensifier, and more particularly to an X-ray image intensifier, wherein that part of the envelope which constitutes an X-ray inlet window is made of aluminium.
The X-ray image intensifier is used to convert and intensify an image provided by X-rays modulated by being penetrated through a subject into a visible image. Hitherto, the X-ray inlet window section and output section of the envelope of an X-ray image intensifier have been made of glass. Further, the X-ray inlet window is demanded to have an area conforming to the size of a subject and generally has as large a diameter as 150 to 300 mm. Since the X-ray image intensifier is highly evacuated, the glass must have a thickness of several millimeters. Accordingly, the conventional X-ray image intensifier has the drawbacks that not only the intensifier as a whole increases in weight due to inclusion of thick glass members, but also incoming X-rays are much attenuated by the thick glass of the X-ray inlet window, and considerably weakened in intensity when reaching a fluorescent layer provided inside of the X-ray inlet window section.
To eliminate the above-mentioned difficulties, an attempt has hitherto been made to reduce loss of incoming X-rays and decrease the weight of an entire X-ray image intensifier by applying an aluminum sheet in place of a glass one to the X-ray image inlet window section. In this case, it is necessary to attain high airtightness for a evacuated envelope used as an X-ray image intensifier by hermetically fusing the X-ray inlet window section with the output section of the envelope. However, aluminium and glass have different expansion coefficients and fail to be fused together. Therefore, an attempt has been made to realize the bonding of both aluminium and glass by means of a joint ring or a coupling made of glass-wettable alloy or alloy fusible with glass commercially known as "Kovar" (trademark of Westinghouse Electric Corp.) which is formed of 29% of nickel, 17% of cobalt and iron as the remainder. Yet, aluminium and Kovar cannot be directly fused together. Therefore, it was proposed, as set forth in the Japanese utility model application published before examination No. 25810/74, to meld together both aluminium and Kovar by inserting a nickel layer therebetween as an intermediate member or an interleave. Further, the Japanese utility model application published before examination No. 14440/75 disclosed application of copper as an intermediate member to attain the bonding of aluminium and Kovar. However, these proposed processes are found unacceptable for the hermetic sealing of an envelope demanded to be kept in high vacuum such as an X-ray image intensifier.